A Study on the Influence of Elevation Stiffness Irregularities on the Seismic Performance of RC Framed Buildings

The history of earthquakes in which numerous reinforced concrete structures were seriously damaged, has indicated the need for gauging the seismic adequacy of buildings. In particular, the seismic rehabilitation of older concrete structures in high seismicity areas is a matter of growing concern, since the structures which are vulnerable to damage must be identified and an acceptable level of safety must be established. To make such an assessment, simplified linear-elastic methods are not adequate. Thus, the structural engineering community has developed a new generation of design and seismic procedures that incorporate performance based design of structures. This is different from simplified linear elastic methods and involves non-linear techniques.� The advancement of performance based design and rehabilitation of structures in high seismic zones reveal that the static non-linear analysis also known as “pushover analysis is the most appropriate method of analysis used to gauge the severity of the damages caused to the buildings. There are two special codes called “ATC-40� and “FEMA-273� which inhibit all the modelling and design procedures and judging criteria of the performances of buildings. Incremental lateral loading is applied to the frame and pushover analysis is carried out using a suitable analysis and design software package such as ETABS. A graph is plotted involving the pushover curves which indicate the capacity of the frame and the seismic demand curves depending on the magnitude of shaking. This graph suggests the seismic performance of a system and its adequacy against the design earthquake.� Later an attempt has been made to understand the seismic behaviour of structures having irregularities in the distribution of structural stiffness in both plan and elevation using pushover analysis. Formation of the plastic hinges and their transformation from elastic level to various seismic performance levels such as immediate occupancy (IO) level, life safety (LS) level, collapse prevention (CP) level and finally collapse (C) level under incremental lateral loading is investigated. For the purpose of carrying out pushover analysis, ETABS v.13, finite element software has been used. ETABS performs the initial design depending on the earthquake zone and formulates the results.